1. Field of Invention
The present invention relates to a fiber optic draw furnace for making optical fiber; and more particularly to liners and heating elements for graphite resistance and inductance furnaces.
2. Discussion of Related Art
Known graphite resistance fiber optic draw furnaces typically have a standard extruded graphite liner or heating element that is nonhomogeneous and low in density. The standard extruded graphite liner or heating element has high porosity (high surface area) that makes its material more reactive with oxygen and silica and more susceptible to erosion from thermal stress. The standard graphite liner or heating element is also susceptible to moisture and oxygen absorption. Nonhomogeneous physical properties can result in uneven heating around the circumference of the preform and can increase the odds of catastrophic failure.
Other known draw furnaces use isomolded graphite liners that are much higher in density than the extruded graphite liners. However, the isomolded graphite is very expensive, which significantly adds to the cost of producing optical fiber.